Conventionally, polyolefins are known as resins excellent in chemical resistance and solvent resistance. However, when polyolefin is low in crystallinity index, it cannot be said that the polyolefin has sufficient rigidity, heat resistance and solvent resistance.
On that account, there is adopted a process for improving polyolefin in heat resistance and rigidity by the addition thereto of a nucleating agent or a process for enhancing polyolefin in crystallinity index by cooling a molten polyolefin gradually. However, it is hard to say that the effect obtained thereby is sufficient.
Apart from such polyolefins as referred to above, it is reported that copolymers obtained by the reaction of ethylene with bulky monomers are excellent in properties such as heat resistance in comparison with conventionally known polyolefins (see, for example, U.S. Pat. No. 2,883,372 and Japanese Patent Publication No. 14910/1971).
In this connection, on the basis of the acquired information on the fact that cyclic random copolymers obtained by copolymerization of specific cycloolefins as bulky monomers and ethylene are excellent in heat resistance, heat aging characteristics, dielectric characteristics and rigidity, the present applicant has already proposed random copolymers obtained by using specific cycloolefins (see Japanese Patent L-O-P Publications Nos. 168708/1985, 120816/1986, 115912/1986, 115916/1986, 271308/1986, 272216/1986, 252406/1987 and 252407/1987).
On the other hand, an attempt has been made to incorporate other resins into polyamides for the purpose of improving characteristics inherent in polyamides. In spite of various improvements suggested as above, there was much room for further improvement on various characteristics such as water absorption properties, molding shrinkage or heat-resisting rigidity.